It is the purpose of this project to investigate the vertebrate host factors which regulate gametogenesis of malaria parasites of the genus Plasmodium and to develop methods for immunizing the vertebrate host against the sexual stages of the parasite which develop in the gut of the mosquito vector. Studies underway are concerned with: 1) biological and biochemical factors which regulate gametocyte maturation and exflagellation; 2) vertebrate factors which enhance or inhibit exflagellation, fertilization and oocyst development in the mosquito gut; 3) development of an efficient method for immunization of the vertebrate host against the sexual stages of the malarial parasite.